Perceptual recognition is a fundamental forms of decision-making. In this project, we propose a set of experiments to investigate the functional neuroanatomy of perceptual decision-making in monkeys and humans using fMRI and behavioral measures to test predictions of the DDM on the effects of stimulus discrimination difficulty, attention, stimulus probability, task, and response modality on neural activity in perceptual and decision-making cortical regions. We have developed the capability to perform fMRI in awake, behaving monkeys, allowing us to run parallel experiments using fMRI in monkeys and humans and single unit recording in monkeys (under project 5). These parallel studies will use the same perceptual decision-making task: motion discrimination with oculomotor response. We will then extend this work with further stimulus and task manipulations. Based on the DDM, we predict that manipulations of stimulus probability, stimulus discrimination difficulty, response modality, and task demands will have differing effects on activity in areas associated with perceptual representation and areas that act as accumulators for decision-making. Using fMRI we will test the predictions of the DDM on the biasing effect induced by manipulating stimulus probabilities in an attention task. We will extend our investigation of the DDM to more complex stimuli, namely faces, in behavioral and fMRI studies. Whereas current application of the DDMto the neuroscience of decision-making assumesthe existence of two populations, each of which codes one of two possible stimuli with a simple rate code, the neural representation of faces and other complex stimuli involves a distributed population response with multiple neural populations. For decisions based on recognition of complex stimuli, perceptual representation must be based on population responses that are translated into a simple code for two alternatives determined by decision task demands. The proposed studies will address whether the DDM can be extended to a model of distributed neural representation.